Isotope separating apparatus



July 28, 1953 w. E. PARKINS ISOTOPE SEPARATING APPARATUS Filed June 14, 1946 QWN J Y W. f w\ M m x r m- \JW MW WW1 1 l HF Qw Patented July 28, 1953 to the United States of America as represented bythe United States Atomic Energy Commissionv Application June 14, 1946, Serial. No. 676,650

Claims. I

My invention relates in general to electromagnetic isotope separation apparatus having apertured accelerating and decelerating electrodes, and more particularly to aperturedaccelerating and decelerating electrodes which are soarranged as to reduce flaring in the direction of the magnetic field in theionbeam projected through such electrodes.

An electromagnetic isotope separation apparatus usuallycomprises a magnetic field, anionization chamber, apertured accelerating and decelerating electrodes which are arranged to project an ion beam ina direction normal to the magnetic field, areceiver adaptedtoreceive the ion beam at the region of geometrical focus, and an envelope adapted to make it possible to evacuate the space within and surrounding the ionization chamber; the apertured accelerating and deceleratin electrodes, and the receiver.

In the operation of the electromagnetic isotope separatingapparatus in combination with straight types of apertured accelerating and decelerating electrodes, elongated in the direction of the magnetic field, a-n appreciablepart'of the ion beam fails to pass into the receiver" due to;

excessive flaring at the edges of the ion beam: as' this ion beam is passing through the-magnetic field on its path to the receiver. This condition necessitates an increase in the receiver width with the subsequent result that the ratio of scattered to unscattered particles in the receiver is increased. An increase in thenumber of scattered particles at thereceiver end results in a: decrease-of the enhancement-of'the final product. It has previously been proposed toeliminate-such flaring by curving the adjacent surfaces of the apertured accelerating and decelerating elec trodes throughout their entire: length,. thus create ing a. curved; electrostatic field betweensaid elect trodes. and causing the. ion beam to. converge, thereby: reducing: the required: receiver width. This solution of? the: flaring condition. resultedin. another problem due to the concentrated. ion beam. thus: formed: being focused; on: the receiver and: producing an; unusually;hot, central portiom. which resulted; in sputtering; of thereceivermas' terial: along with. some sputtering: oft previously: separated; ion. beam particles; which. had? been. deposited thereon.

An object; of: my. invention: is to. substantially:

reducethe sputtering of thewre'cei ver material and the'separated ionbeam particles deposited thereon'byusing apertured:accelerating and decelerat ingelectrodes having straight central adjacent faces with curved adjacent faces at their ex-tremi ties to create an electrostatic field which will focus the ion beam in such a manner as to result in a more equally distributed ion beam at the receiver.

Another object of my invention. is to prevent excessive flaring in the edges of the ion beam by curving the faces of the apertured accelerating and decelerating apertures at their'extremi'ties'so as to create an electrostatic field which will focus the edges of the ion beam towards the center of the receiver.

My invention successfully overcomes the flaring of the ion beam, while substantially reducingthe sputtering of the receiver rr-i'aterial and the sepa rated ion beam particles deposited thereon, by allowing the central adjacent portions of the apertured accelerating and decelerating electrodes to remain straight while the adjacent extremitiesofthe same apertured accelerating and decelerating electrodes are-curved, this extremity curvature being; concave toward thev ionization chamber for bothof the adjacent facesof the? apertured accelerating and decelerating elecftrodes. By localizing the focusing action tofithe edges of" the ion beam; whilethe central portion of thei'on beam remainsrelatively'unafiecte'di my invention avoids the concentration of the ion beam at" the center of the receiver and prevents the excessive sputtering action which normally results therefrom.

These and other important feature of my in vention will be-und'erstoodmore"- thoroughly from"- the following description when taken in-conjunc tion with the accompanying drawing, the single figure-of which shows schematically a develop--* ment of a conventionalized electromagnetic iso topeseparator incorporating the invention.

Withreference to the drawing, positive ions produced an ionchamber I 8 tend to travelto wards theaperture of an accelerating'electrode- H'- in paths approximately normal toequipotentiallines [3 which exist between the aperturedaccel era-ting electrode H' and" the ion chamber In. After the positive ions pass through the aperture or the accelerating electrode. II, theyfind" themselves in a decelerating electric field represented by equipotential' lines M which exist. between the apertured accelerating electrode I I and. an aper! tured' decelerating. electrode. l2. The equipoten; tial lines ll of the decelerating electric field are curved in. the region between the extremities. of" theadja'cent' electrode faces. due to the extremity curvature of the adjacent faces of the apert'ured'i accelerating'electrode I If andthe apertured .deceleratingelectrode- I '2; In' theregibn of thed'ecelenating electric field the ion beam, a represented by a series of ion paths ll, tends to bend away from the normal to the equipotential lines l4, thereby resulting in a focusing action being exerted on the ion paths H which exist at the edges of the ion beam as formed by the aggregate ion beam paths. This focusing action results in a reduction of the width of the ion beam and thereby permits the use of an ion receiver [8 having less width than one which is required when straight apertured accelerating and decelerating electrodes are used.

Again referring to the drawing, a detailed discussion of the operational features of the invention and the cooperating elements involved follows:

Positive ions of the material to be separated by the electromagnetic isotope separation apparatus are produced in the ion chamber by bombardment of unseparated material in the vapor state by an electron beam. The electron beam is normally produced by an electrically heated filament, not shown in the drawing, which is maintained at a negative potential with respect to the ion chamber It. maintained at a positive potential of approximately kv. with respect to ground potential. The apertured accelerating electrode I I is maintained at negative potentials of between 15-40 kv. with respect to ground potential, thus placing the apertured accelerating electrode H at negative potentials of between -75 kv. with respect to the potential of the ion chamber H3. The apertured decelerating electrode I2 is connected to ground potential.

The arrangement of the aforementioned potentials creates an accelerating electric field for positive ions when they are in the region between the ion chamber l0 and the apertured accelerating electrode H, while it creates a decelerating electric field for the positive ions when they are in the region between the apertured acceleratingv electrode H and the apertured decelerating electrode l2.

' The adjacent faces of the ion chamber In and the apertured accelerating electrode H are approximately parallel to each other and to the direction of a magnetic field i5 which exists throughout an inclosing envelope it. Therefore,

the equipotential lines l3, which represent the accelerating electric field, will be approximately parallel to the direction of the magnetic field i5 and the adjacent faces of the ion chamber l0 and the apertured accelerating electrode ll. Since in an accelerating electric field, charged particles, such as the positive ions created in the ion chamber lil, will tend to traverse paths which are approximately normal to the equipotential lines l3 of the accelerating electric field, the positive ions will therefore assume paths which will be approximately normal to the direction of the magnetic field '15 and the adjacent faces of the ion chamber In and the apertured accelerating electrode H.

The adjacent faces of the apertured acceleratingf electrode II and the apertured decelerating electrode l2 are approximately parallel to each other throughout their entire length, but only their central portion, which is approximately equal to one-third of their entire length, is approximately parallel to the direction of the magnetic field l5. The two extremities of the adjacent faces of the apertured accelerating electrode II and the apertured decelerating electrode l2, consisting of approximately one-third of the elec- The ion chamber 10 is 4 trode length for each extremity, are curved lengthwise and concave towards the source of the ion beam for both of said electrodes. The centers for the extremity curvatures fall on a line normal to the electrodes at their mid-points in the direction of the ion chamber to, and the radii of curvatures required are dependent upon operating voltages, magnetic field strengths, electrode spacings, and upon the degree of focusing desired. The same radius of curvature is used for each electrode. The equipotential lines 14, which represent the decelerating electric field between the apertured accelerating electrode l I and the apertured decelerating electrode 12, will assume approximately the same configuration in the space between the electrodes as the adjacent surfaces of the apertured accelerating electrode H and the apertured decelerating electrode I2; i. e., the equipotential lines l4 will be curved in the horizontal plane at the two extremities between the electrode H and the electrode [2 and the central portion will be straight and approximately parallel to the direction of the magnetic field l5. Since, in a decelerating electric field, ion paths which are not initially normal to the equipotential lines I4, tend to bend further away from the normal, the edges of the ion beam, which is formed by the aggregate ion paths I! from the ion chamber I9, will have a focusing action exerted upon them. The central portion of the ion beam, which is directed approximately normal to the central section of the equipotential lines M, will be relatively unaffected as to direction of travel while passing between the electrode I! and the electrode l2.

The focusing efiect at the edges of the ion beam due to the curved extremities of the apertured accelerating electrode l l and the apertured decelerating electrode 12 permits a reduction of the receiver width, which, in turn, results in an increase in the enhancement by virtue of an increase in the ratio of unscattered to scattered particles. The straight central portion of the apertured accelerating electrode H and the apertured decelerating electrode I2 results in a more equally distributed beam. at the receiver end, thus preventing excessive sputtering of the receiver material and separated particles which may be deposited thereon, which, in turn, means longer receiver life at higher enhancements,

It will be appreciated that the ion beam in traversing the distance between the electrode l2 and the receiver IE will have followed a circular orbit for approximately in a plane normal to the magnetic field l5.

It will be obvious to those skilled in the art that changes and variations may be made in this apparatus without departing from the spirit of the invention, and therefore the invention herein described is not limited to what is shown in the drawing and described in the specification but only as indicated by the appended claims.

I claim: i

1. In electromagnetic isotope separating apparatus, in combination, an evacuated tank, means for establishing a magnetic field traversing said tank in a given direction, an ion source disposed within and at one end of said tank and having an elongated slot for the egress of ions, said slot extending in the direction of the magnetic field, means adjacent said source for accelerating and projecting positive ions emanating from said slot through the magnetic field in a direction normal thereto and in the form of a ribbon beam elongated in the direction of said field, said last named means comprising two spaced electrodes having slots generally coextensive with the slot of said ion source and also elongated in the direction of the magnetic field, the facing surfaces of said two electrodes being concave toward said ion source at their end portions only, and means for maintaining the outer of said electrodes at a negative potential with respect to said ion source and at a positive potential with respect to said inner electrode, and ion beam receiving means disposed within and at the opposite end of said tank, said receiving means also being elongated in the direction of the magnetic field.

2. Apparatus, as claimed in claim 1, wherein the facing surfaces of said two electrodes each have central sections which are straight and parallel to the magnetic field.

3. Apparatus, as claimed in claim 2, wherein the length of each of said straight central sections is approximately one-third of the entire length of said surfaces.

4. In electromagnetic isotope separating apparatus, in combination, an evacuated tank, means for establishing a magnetic field traversing said tank in a given direction, an ion source disposed within and at one end of said tank and having an elongated slot for the egress of ions, said slot extending in the direction of the magnetic field, means adjacent said source for accelerating and projecting positive ions emanating from said slot through the magnetic field in a direction normal thereto and in the form of a ribbon beam elongated in the direction of said field, said last named means comprising a first apertured electrode having an elongated surface facing and paralleling the slot of said ion source and having an opposite surface the central portion of which parallels the slot in said ion source and the end portions of which are cylindrically concave toward said ion source, a second apertured electrode having an elongated surface facing and being a matrix image of said opposite surface of said first electrode and having an opposite surface paralleling the slot in said ion source, and means for maintaining said second electrode at a negative potential with respect to said ion source and at a positive potential with respect to said first electrode, and ion beam receiving means disposed within and at the opposite end of said tank, said receiving means also being elongated in the direction of the magnetic field.

5. Apparatus, as claimed in claim 4, wherein the length of said central portion is approximately one-third the entire length of said opposite surface of said first electrode.

WILLIAM E. PARKINS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,378,962 Washbum June 26, 1945 2,412,687 Klemperer Dec. 17, 1946 

